Piezoelectric Ultracapacitor

ABSTRACT

Piezoelectric ultracapacitor is disclosed capable of converting the kinetic energy of ordinary motion into an electrical potential. The piezoelectric ultracapacitor of the present invention may be used in various contexts, including power generation, switching and control and memory.

BACKGROUND OF THE INVENTION

The generation of energy is a substantial concern to governments,individuals and research bodies around the world because of thedifficulty in securing sufficient fuels to meet rising energy demand andthe many environmental hazards associated with the generation of powerand the acquisition of fuels stocks. One need only consider the MiddleEast or the tailpipe of an automobile to begin to appreciate theproblems involved with the current approach to energy generation.

Many have attempted to develop acceptable alternatives to fossil ornuclear fuels, with limited success. Solar, wave and wind energysystems, for example, provide mechanisms by which electrical energy canbe generated without the use of fossil fuels, but they suffer from beingsubject to the variability of the weather and also are only economicallymarginal as a replacement to fossil fuels. Similarly, techniques formaking fuel from renewable biological sources, such as ethanol from cornor sugar cane, have been developed, but present difficulties of theirown, including the diversion of agricultural land from food productionand relatively limited energy production.

Fusion, of course, is yet another energy generation technique that holdsgreat promise, but that promise is far in the future and is unlikely tobe realized in a practical way for many decades, if ever.

What would be ideal, and is needed, is an energy generation technologyemploying an abundant input, providing potentially significant energyoutput, avoiding environmental hazards and which is readily deployable.

SUMMARY OF THE INVENTION

These and other needs are satisfied by the present invention, whichemploys a piezoelectric ultracapacitor to harness efficiently the energyin physical motion, such as walking, driving or vibrating. Apiezoelectric element continuously creates a potential difference inresponse to physical forces exerted on it, including forces exerted bythe ordinary vibrations of everyday life. The potential differencecauses charge to accumulate on an ultracapacitive structure, whichcharge is prevented from returning to the piezoelectric by one or moresemiconductive devices.

While some have attempted in the past to use piezoelectrics for energygeneration, it is well-known that piezoelectric materials createvoltages of very limited duration and extremely small currents, therebylimiting their ability to generate electric power. Ultracapacitors, ofcourse, have also been known and used in various contexts for energystorage, but not, to the inventor's knowledge, for energy generationpurposes. The combination of piezoelectric and ultracapacitortechnologies, such as in the manner described herein, provides not onlypotential differences of extended duration, but also unexpectedlyexhibits the ability to regenerate the charge captured on theultracapacitive structure even after that charge has been drained awayfor other purposes. The present invention thus provides a constantvoltage source without the use of fossil fuels, or any of the otherdisadvantages associated with the technologies described above. Such avoltage can be used for power generation, control and other purposes aswill become apparent to those of ordinary skill in the art in view ofthe disclosures below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a first embodiment of a piezoelectric ultracapacitoremploying the principles of the invention.

FIG. 2 depicts a second embodiment of a piezoelectric ultracapacitoremploying the principles of the invention.

FIG. 3 depicts a third embodiment of a piezoelectric ultracapacitoremploying the principles of the invention.

FIG. 3 a depicts a modification of the embodiment of a piezoelectricultracapacitor shown in FIG. 3.

FIG. 4 depicts a fourth embodiment of a piezoelectric ultracapacitoremploying the principles of the invention.

FIG. 5 depicts a fifth embodiment of a piezoelectric ultracapacitoremploying the principles of the invention.

DETAILED DESCRIPTION

Referring to FIG. 1, piezoelectric element 101 is coupled toultracapacitor 107 through diodes 105 and 106. Piezoelectric element 101can be formed of one or more portions of one or more suitablepiezoelectric material, such as polyvinylidene difluoride (known as“PVDF”) or flexible lead zirconate titanate (often referred to as“PZT”). The invention is not limited to the use of these materials,though it is believed that the flexible nature of these twopiezoelectric materials provides some protection from cracking or otherdamage during use. Flexible piezoelectric materials are thereforepreferred.

Moreover, experiments have unexpectedly shown that the power generationcapability of the present invention is not greatly enhanced by the useof PZT (which is inherently capable of creating higher voltages thanPVDF); PVDF is therefore preferred due to its lower cost. Such materialsare known and commercially available from many different sources. PVDF,for example, is available commercially under the trade names KYNAR® andKYNAR FLEX® by Arkema, Inc. of Philadelphia, Pa.

In this and other embodiments that follow diodes are described ascoupling the piezoelectric element to electrodes of the ultracapacitor.However, other coupling mechanisms, such as FET or BJT transistors, canbe employed. Indeed, in many applications the use of transistors insteadof diodes may be preferred because of the switching capability theyprovide.

Ultracapacitor 107 is formed from electrodes 102, formed for examplefrom aluminum; electrolyte materials 103, such as cotton cloth or othermaterial impregnated with an electrolytic solution (a solution of sodiumchloride in water, for example); and barrier 104, which can be a protonconductor such as Nafion, a commercially available proton conductivemembrane manufactured by the DuPont Company of Wilmington, Del. anddistributed by Ion Power, Inc. of New Castle, Del. Ultracapacitors havebeen known for some time, and appear to have been invented at theGeneral Electric Company in the late 1950's. See, for example, U.S. Pat.No. 2,800,616, the entirety of which is hereby incorporated byreference. The principles of their operation are therefore well-known tothe art and will not be further explained here.

It should be noted, however, that modern ultracapacitors often employ aproton conductive barrier, such as the aforementioned Nafion, but such abarrier is not necessary to the formation of an ultracapacitor. It hasbeen found that such a barrier is not necessary for implementation ofthe present invention either and indeed adds only a small amount ofadded efficiency. Thus, while some of the embodiments of the inventionare here described as including such a barrier/membrane, it should berecognized that such a barrier is not a requirement of the inventionexcept where specifically and expressly called for by the claimsappended hereto.

Referring again to FIG. 1, in operation, forces exerted on thepiezoelectric element 101, from vibrations or other movements, induce avoltage across the surfaces of element 101, which is applied to theultracapacitor through the coupling shown. Such voltages can besubstantial though, as noted above, the current created by piezoelectricmaterials is quite small, due to the extremely high input impedance ofthe piezoelectric material and the fleeting nature of the potentialdifferences. Nevertheless, the voltage causes a charge to accumulate onthe electrodes of the ultracapacitor, charge that is prevented fromreturning to the piezoelectric element by diodes 105 and 106.

Charge accumulated on the electrodes 102 of the ultracapacitor cause anopposite charge to accumulate at the interface of the electrolyticmaterials and the electrodes. Charge carriers in an electrolyte areions, not electrons, so they are incapable of traveling through themetal structure of the electrodes. Instead, the interface between theelectrode and the electrolyte, on each side of the ultracapacitor 107(i.e., the bottom and top as shown in the figure) acts as a highly densecapacitor capable of storing a very large amount of energy and providingto relatively stable potential difference, designated as V_(out). Outputnodes are shown across each of the diodes 105 and 106, across whichV_(out+) and V_(out−), respectively, can be obtained.

Either of these output voltages can be coupled to a power consumptiondevice. For example, the energy stored in the ultracapacitive structurescan be drained off, to be stored in another circuit element, such as abattery or capacitor. Alternatively, either output voltage may also beused as a control voltage, such as in a logic circuit, or for purposesof performing some work in an electrical, chemical or mechanical device,such as a solar cell, a fuel cell or an alarm, respectively.

Referring now to FIG. 2, there is shown a second embodiment, 207, of apiezoelectric ultracapacitor employing the principles of the invention.There, piezoelectric element 201 forms the center barrier ofpiezoelectric ultracapacitor 207, and is coupled to electrodes 202through diodes 205 and 206. Electrodes 202 are similar to electrodes 102described in connection with FIG. 1. Electrolyte materials 203, whichseparate piezoelectric element 201 from electrodes 202, are also similarto electrolyte materials 103 described in connection with FIG. 1.

The positive and negative faces of the element 201 are indicated in thefigure (as they are in the other figures as well). Those of ordinaryskill in the art will understand that the proper coupling of diodes 205and 206 depends on which face of the piezoelectric element the diode isbeing coupled to. Thus, diode 205 is coupled to the negative face ofpiezoelectric 201 through its cathode and diode 206 is coupled to thepositive face of the piezoelectric through its anode. Similar couplingsare depicted in each of the figures.

The operation of the embodiment shown in FIG. 2 is also similar to theoperation of the embodiment shown in FIG. 1, though with somedifferences. More specifically, forces exerted on piezoelectricultracapacitor 207, and thereby on piezoelectric element 201, induce avoltage across the surfaces of element 201, which voltage is applied tothe electrodes 202 through the coupling shown, including diodes 205 and206. The voltage causes a charge to accumulate on the electrodes of theultracapacitor, charge that is prevented from returning to thepiezoelectric element by diodes 205 and 206. As with the embodiment ofFIG. 1, charge accumulated on the electrodes 202 of the ultracapacitor207 causes an opposite charge to accumulate in the electrolyticmaterials at the interface of those materials with the electrodes,thereby again causing each interface to become a very dense capacitor.

FIG. 3 depicts yet another embodiment of the invention, here configuredas a two-sided ultracapacitor. Specifically, there is shownpiezoelectric ultracapacitor 307 having piezoelectric element 301 thatforms the center barrier of piezoelectric ultracapacitor 307, and iscoupled to electrodes 302 through diodes 305 and 306. Electrodes 302 aresimilar to electrodes 102 described in connection with FIG. 1.Electrolyte materials 303, which separate piezoelectric element 301 fromelectrodes 302, are also similar to electrolyte materials 103 describedin connection with FIG. 1. Here, however, electrolyte materials 303 eachcomprise two electrolytic sub-materials separated by proton conductivemembrane 304 to provide further separation of negative and positive ionsin the electrolyte.

It should be noted that the invention does not require formation of atwo-sided ultracapacitor as shown in these figures. A one-sidedultracapacitor—for example, one including only the top half of FIG.3—would also be encompassed by the invention. Such an embodiment isshown in FIG. 3 a, and those of ordinary skill in the art will readilyunderstand how to make and use a one-side ultracapacitor in the contextof the other embodiments described herein.

FIG. 4 depicts yet another embodiment, which is a modification of theembodiment shown in FIG. 3. Here, multiple ultracapacitive layers areformed above and below each face of the piezoelectric element. Thepiezoelectric ultracapacitive stack of this embodiment includes multipleelectrolytic sub-layers (403 a-h), multiple electrode sub-layers (402a-d) and multiple proton conductive sub-layers (404 a-d). The samematerials described above may be employed for these sub-layers.Sub-layers 402 a and 402 c are coupled together and to the cathode of adiode 406, and thereby to the positive face of piezoelectric element401. Layers 402 b and 402 d are coupled together and to the anode ofanother diode 405, and thereby to the negative face of piezoelectricelement 401.

Note that in such an embodiment diodes 405 and 406 are each coupled tomultiple electrode layers in the stack. It is, of course, possible toemploy multiple semiconductive elements coupled to each face of thepiezoelectric—one per electrode for example. However, where the combinedmaximum voltage created on all electrodes coupled to a single face ofthe piezoelectric is less than the breakdown voltage of the diode, it ismore efficient to employ just a single diode per piezoelectric face, asshown.

FIG. 5 depicts an embodiment similar to that of FIG. 4, but here theproton conductive layer is not included in the capacitive layersimmediately adjacent to the piezoelectric element. Of course, the protonconductive layer could have been left out of the outer capacitive layersas well.

One important benefit of the structures described above is their abilityto recharge themselves. Taking the structure of FIG. 2 as an example,once piezoelectric ultracapacitor 207 is charged to a maximum, thatcharge may be drained, as mentioned above, either to some energy storagemechanism, such as a battery or capacitor, or to perform some work.However, once drained the charge across each diode 205 and 206 returns,over the course of several seconds, without further intentionalexcitation or the connection of some other power source. Thepiezoelectric element is constantly creating continually varyingvoltages due to the normal—though usually unnoticed—vibrations and otherforces of ordinary life. Those voltages, though relatively small, induceconcomitant charge accumulations on electrodes 202 and, due to thesemiconductive properties of diode 205 and 206, eventually charge thepiezoelectric ultracapacitor 207 to a maximum level. In experimentsusing an embodiment that employed aluminum electrodes, cotton clothimpregnated with a sodium chloride solution for the electrolyte 203 anda PZT element at the core, it was observed that recharging of each sideof the piezoelectric ultracapacitor to about 0.3V occurred in about 3seconds. A similar capability was observed in an embodiment similar tothat of FIG. 2 and employing a PVDF core.

The embodiments described above are, of course, exemplary and notintended to limit the scope of the claims beyond that which isspecifically and expressly stated in the claims.

1. A piezoelectric device, comprising: a piezoelectric element coupledto a first electrolyte material, said first electrolyte material coupledto a first electrode, and said piezoelectric element electricallycoupled to said first electrode.
 2. The piezoelectric device of claim 1wherein said piezoelectric element is further coupled to a secondelectrolyte material, said second electrolyte material coupled to asecond electrode, and said piezoelectric element electrically coupled tosaid second electrode.
 3. The piezoelectric device of claim 1 where insaid first electrolyte material includes a first proton conductivemembrane.
 4. The piezoelectric device of claim 1 wherein saidpiezoelectric element is comprised of at least one flexiblepiezoelectric material.
 5. The piezoelectric device of claim 1 whereinsaid piezoelectric element is electrically coupled to said firstelectrode via a first semi-conductive device.
 6. The piezoelectricdevice of claim 2 wherein said piezoelectric element is electricallycoupled to said first electrode via a first semi-conductive device andelectrically coupled to said second electrode via a secondsemi-conductive device.
 7. The piezoelectric device of claim 5electrically coupled to a means for storing energy.
 8. The piezoelectricdevice of claim 5 electrically coupled to a means for performing work.9. The piezoelectric device of claim 5 electrically coupled to a means,for controlling.
 10. An ultracapacitive device, comprising: a firstconductor, coupled to a first electrolyte layer, said first electrolytelayer coupled to a first face of a piezoelectric element, a secondconductor, coupled to a second electrolyte layer, said secondelectrolyte layer coupled to a second face of said piezoelectricelement, said first face of said piezoelectric element electricallycoupled to said second conductor through a first semi-conductive deviceand said second face of said piezoelectric element electrically coupledto said first conductor through a second semi-conductive device.
 11. Theultracapacitive device of claim 10 further comprising a third conductorcoupled to a third electrolyte layer, said third electrolyte layercoupled to said first conductor, and said second face of saidpiezoelectric element electrically coupled to said third conductor. 12.The ultracapacitive device of claim 11 wherein said second conductor andsaid third conductor are both coupled to said second face of saidpiezoelectric element through said second semi-conductive device. 13.The ultracapacitive device of claim 12 further comprising a fourthconductor coupled to a fourth electrolyte layer, said fourth electrolytelayer coupled to said second conductor, and said first face of saidpiezoelectric element electrically coupled to said fourth conductor. 14.The ultracapacitive device of claim 13 wherein said first conductor andsaid fourth conductor are both coupled to said first face of saidpiezoelectric element through said first semi-conductive device.
 15. Amethod of forming a piezoelectric ultracapacitor, comprising thefollowing steps in any order: (a) coupling a first conductive layer to afirst electrolyte layer; (b) coupling said first electrolyte layer to afirst face of a piezoelectric element; (c) coupling a second conductivelayer to a second electrolyte layer; (d) coupling said secondelectrolyte layer to a second face of said piezoelectric element; (e)coupling said first face of said piezoelectric element to said secondconductive layer, and (f) coupling said second face of saidpiezoelectric element to said first conductive layer.
 16. The method ofclaim 16 further comprising the step of coupling said piezoelectricultracapacitor to a means for consuming power.
 17. The method of claim16 further comprising the formation of at least one additionalultracapacitive layer coupled to said first conductive layer.
 18. Themethod of claim 16 wherein said piezoelectric element is comprised of atleast one flexible piezoelectric material.
 19. The method of claim 16further comprising the formation of multiple additional ultracapacitivelayers coupled to said first conductive layer and the formation ofmultiple additional ultracapacitive layers coupled to said secondconductive layer.
 20. The method of claim 16 further comprising couplingsaid first face of said piezoelectric element to a first plurality ofconductive layers through a first conductive device and said second faceof said piezoelectric element to a second plurality of conductive layersthrough a second conductive device.
 21. The method of claim 16 furthercomprising coupling said first face of said piezoelectric element to afirst plurality of conductive layers through a first plurality ofconductive devices and coupling said second face of said piezoelectricelement to a second plurality of conductive layers through a secondplurality of conductive devices.